National Planning Policy in England over the last decade has undergone several phases of revision. Among the changes relevant to archaeology has been shifting emphasis regarding the balance of the importance of an archaeological ‘asset’ (for example, a site in common parlance), and the impacts upon that site that would arise from a proposed development.
This can be of fundamental importance in judgments of the extent of mitigation excavations, and hence the costs of such works, with serious implications for financial viability for proposed developments.
The current National Planning Policy Framework (NPPF; updated on 19 February 2019, Last updated 19 June 2019, accessed 12 August 2020) has this whole issue encapsulated in a single paragraph thus:
199. Local planning authorities should require developers to record and advance understanding of the significance of any heritage assets to be lost (wholly or in part) in a manner proportionate to their importance and the impact, and to make this evidence (and any archive generated) publicly accessible. However, the ability to record evidence of our past should not be a factor in deciding whether such loss should be permitted.
The key phrase is, “A manner proportionate to their importance and the impact”. This suggests a more-or-less equal balancing of the two axes – the more important a site, the greater the extent of impact leading to the greater investment in archaeological mitigation. And the reverse would be true: a less important site with minimal impacts should mean minimal mitigation.
There are no universal methods for reaching a judgment, but there are one or two widely used and widely consulted-upon processes such as the venerable Highways Agency Design Manual for Roads and Bridges (DMRB; accessed 12-08-2020: LA106 revision replaces the earlier HA 208/07, HA 75/01 and HA 60/92 versions). In the current guide LA104 Table, 3.2N sets out a general scheme for assessing importance and Table 3.4N sets of a scheme for assessing impacts, while the balancing of importance and impacts is achieved by a simple matrix in Table 3.8.1.
For the moment, let’s side-step judgments of significance and focus on impacts. A ‘minor’ impacts is described as “Some measurable change in attributes, quality or vulnerability; minor loss of, or alteration to, one (maybe more) key characteristics, features or elements.” A moderate impact involves a “partial loss of/damage to key characteristics, features or elements”. Inherent in all this is the assessment that adverse impacts must involve some degree of direct physical loss or damage to the archaeology.
Triskelion is working (in August 2020) on sites in 2 Midlands authorities where the local authority has required archaeological excavations in advance of development. The potential or demonstrated importance of the archaeology is not, for present purposes, questioned.
In the clearest – or most egregious – example, the archaeological remains are located at about 400mm below current/existing ground level (this is fairly typical). However, because the site, intended for several hundred new homes, is low-lying, the proposed development involves raising the ground level by about 1500mm to a formation level for construction, plus 300mm of imported topsoil to reach a finished ground level about 1800mm about the present surface. In this design, even the proposed drainage system, at 1000-1200mm below finished ground level will be 1000mm – one metre – above the archaeology.
In summary: no direct physical impacts upon the archaeological remains. Where in this is the justification for requiring an excavation as a condition upon a consent?